Some commercial heating, ventilation, and air-conditioning (HVAC) systems include multiple fans and electric motors in multiple units that work together to provide heating and cooling to a building. For example, the air conditioning or refrigeration systems in many large buildings include multiple condenser units that are located on the roof of the building. Each condenser unit includes an electric motor that drives a fan to direct air over a radiator to cool and condense a refrigerant from a vapor phase to a liquid phase.
In many HVAC systems, multiple motorized units, such as condensers, operate in tandem to provide sufficient cooling capacity for a building or other facility. A central control unit is connected to the fan motors in each of the condenser units and is configured to activate the fan motors, deactivate the fan motors, and adjust the operating speed of the fan motors based on the cooling requirements of the building.
One challenge confronting HVAC systems that include multiple condenser units or other units that include electric motors is the operation of the individual units in an energy efficient manner. For example, in one existing HVAC system, a central controller can operate the fans in multiple condenser units at different speeds, but all of the fans must operate at the same speed. In some operating conditions, the HVAC system could operate more efficiently if only some of the motors operated simultaneously. In another embodiment, a single controller operates the fan in a single condenser unit, then the control signal from the controller is propagated to a second fan motor in a second condenser unit at a lower level, to a third motor in a third fan unit at still a lower level, etc. to enable a single control unit to operate the fans in multiple condenser units at different speeds. One drawback of the aforementioned system is that the controller is unable to operate the fans in all of the condenser units at a maximum speed in situations where the HVAC system is required to operate at high capacity.
One approach that controls multiple fan motors at different speeds includes a controller that communicates with each motor individually, either through individual control lines or through a digital control system that communicates using, for example, wired or wireless digital networking. While such systems are known to the art, the added complexity required in the controller and the added infrastructure required to run individual control wires or add digital control systems to the motors in existing HVAC units adds to the cost and maintenance burden for building and operating the HVAC system. Consequently, improvements to HVAC control systems that enable operating different motors in the HVAC system over a full range of different operating speeds during operation without requiring generation of individual control command signals for each motor would be beneficial.